Golubev et al., in U.S.S.R. Inventor Certificate No. 341,788, disclose a liquid phase process for producing 1,1-difluoroethane (HFC-152a) by reacting chloroethene with hydrogen fluoride (HF) while in the presence of tin tetrachloride (SnCl.sub.4).
Komatsu et al., in European Patent EP 187,643, disclose a process for manufacturing hydrofluorocarbons (HFCs) by reacting hydrochlorocarbons (HCCs) with HF while in the presence of a tin catalyst and an additive chosen from compounds containing oxygen or nitrogen.
Komatsu et al., in U.S. Pat. No. 4,766,258, disclose a process for the manufacture of HFCs and hydrochlorofluorocarbons (HCFCs) by allowing HCCs to react with anhydrous HF in the presence of a tin catalyst and an additive chosen from compounds containing oxygen or nitrogen.
Franklin et al., in U.S. Pat. No. 4,968,850, disclose a process for the preparation of HFCs and HCFCs by allowing an unsaturated HCC to react with HF in a liquid phase in the presence of a tin catalyst and an organophosphorous additive.
Komatsu et al., in Japanese Kokai publication number SHO 621987!-246528, disclose a process for the manufacture of HFCs and HCFCs characterized by allowing a hydrogen-containing halogenated hydrocarbon to react with HF in a liquid phase in the presence of the reaction product from a compound acting as a base in HF, a tin catalyst, and HF.
Pennetreau et al., in European patent application EP 637,579, disclose a method for the preparation of either 1-chloro-1-fluoroethane (HCFC-151a) or HFC-152a by reaction of chloroethene with HF in the presence of a metal catalyst and an organic solvent composed of at least one saturated halogenated hydrocarbon.
1,1-Difluoroethane, hereinafter referred to as HFC-152a or 152a, is a compound of considerable utility. It may be used either alone or in blends with other materials as a refrigerant, blowing agent, propellant, cleaning agent, or as an intermediate for other fluorocarbon compounds, such as fluoroethene. HFCs such as HFC-152a are environmentally acceptable replacements for chlorofluorocarbons (CFCs), since they have no known effect on the earth's stratospheric ozone.
Processes for preparing HFCs and HCFCs from HCCs and HF by metal mediated halogen exchange have found wide industrial utility. The overall process is one in which carbon to chlorine bonds of the HCC are broken and carbon to fluorine bonds are formed in their place. The metal acts in a catalytic capacity leading to a more productive exchange process requiring milder reaction conditions. HFC-152a has been manufactured in this manner using liquid and gas phase processes. The literature reveals that HFC-152a has been prepared by allowing chloroethene to react with HF in the presence of salts of various oxidized metals such as tin(IV), titanium(IV), antimony(III), and antimony(V).
Intermediates in the conventional procedures in which HFC-152a is prepared from chloroethene comprise 1-chloro-1-fluoroethane (HCFC-151a, or 151a) and 1,1-dichloroethane (HCC-150a, or 150a). Byproducts of such conventional procedures include an assortment of oligomeric and polymeric materials; low molecular weight halogenated dimers and oligomers through higher molecular weight halogenated polymers taking the form of oils, tars, and dark carbonaceous solids. These byproducts are typically higher molecular weight, e.g., predominately 50,000, with standard weight fraction distribution from 2,000 to 75,000 number averaged molecular weight, branched, polymeric, halogenated hydrocarbons, which may contain metal species acquired from catalyst and other additives, if present. Such higher molecular weight materials can be formed by polymerization of lower molecular weight dimers, trimers, and oligomers with themselves or with the halogenated carbon-containing reagents and their fluorinated adducts. These byproducts are detrimental to the exchange process as they interfere with catalyst activity, reduce reactor volume, decrease the yield of HFC-152a, and are a disposal concern.
Modification of the metal catalyst through addition of compounds which are inert to fluorination but reactive with the metal species in HF, leads to catalysts with different properties from the parent. The ideal additive for the exchange process is one which minimizes byproduct formation while enhancing the reaction rate and increasing selectivity towards the desired product.
Conventional processes for making HFC-152a are undesirable due to the high amounts of tars produced. The inventive process solves the problems associated with conventional processes by reducing the tar formation rates.